Survival Motor Neuron (SMN) copy number distribution in Mali, West Africa
Open AccessAbstract of DissertationSurvival Motor Neuron (SMN) Copy Number Distribution in Mali, West AfricaSMA (spinal muscular atrophy) is the leading inherited cause of infant mortality, with an estimated incidence of one in 6,000 to 10,000 live births and a carrier frequency of 1/30 to 1/50 in populations of European and Asian ancestry. SMA has been thought of as a pan-ethnic disease with similar carrier frequencies throughout the world. However, studies in people with black African ancestry have shown a lower incidence of SMA type 1, a lower SMA carrier frequency, and an unexpectedly high rate of alleles with three or more SMN1 copies (Hendrickson et al. 2009). We did an observational study in 630 Malian healthy controls and found a significantly higher proportion of individuals with three or more SMN1 copies, a higher proportion of individuals with no SMN2 copies and a lower estimated SMA carrier frequency than reported in Eurasians. These findings were confirmed in samples from the Yoruba ethnic group of Nigeria in West Africa and the Luhya ethnic group of Kenya in East Africa. The proportion of hybrid SMN genes in Malians was higher than in Caucasians, but not enough to explain the difference in SMN1 and SMN2 copy numbers. There was no association of increased SMN1 copy number with episodes of severe malaria indicating that the copy number difference is not due to selective pressure from malaria. Increased SMN1 copy number did not translate into increased SMN mRNA in fibroblasts or lymphoblasts. However, studies in human induced pluripotent stem cells from healthy controls suggested an increase in SMN mRNA with increased SMN1 copy number.
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